Method and device for bonding a contact wire to a semiconductor member

ABSTRACT

1,010,016. Welding by pressure; shearing. SIEMENS &amp; HALSKE A.G. July 15, 1964 [July 23, 1963], No. 29287/64. Headings B3R and B3W. [Also in Division H1] A method of attaching a wire 6 to a semiconductor (not shown) by heat and pressure comprises feeding the wire through a nozzle 5 by which it is pressed against the semi-conductor, and severing the attached wire by shearing blades 8, 9, the blade 8 having a cutting edge located intermediate its thickness and a cam surface 15 for bending over the end of wire remaining in the nozzle so as to prepare the wire for a further attaching operation. When the cutting edges meet, a further cam surface 13 on blade 8 deflects the blade 9, Fig. 6, causing it to pass beneath blade 8. A block 14 guides and/or limits movement of the blade, through contact with the nozzle. The block 14 may be interchangeable or adjustable in order to vary the severance plane. The nozzle 5 may be of glass and the wire 6 of gold.

H. KOLLNER 3,239,452 DEVICE FOR BONDING A CONTACT WIRE 0 A SEMICONDUCTOR MEMBER Filed June 5. 1964 Dec. 6, 1966 METHOD AND United States Patent s 86, Claims. of. 72-324 My invention relates to a method and means of bonding a contact wire to a semiconductor member by thermocompression requiring a simultaneous application of pressure and heat, the temperature being below the melting point of the metal and semiconductor substance that are to be thus bonded to each other.

In a more particular aspect, the invention relates to thermocompression method and apparatus of the type in which the wire to be attached to the semiconductor bodies is supplied through a guiding nozzle toward the semiconductor surface. The wire end protruding from the nozzle opening is pressed onto the semiconductor surface by forcing the suitably shaped lower nozzle edge against the surface and simultaneously subjecting the semiconductor and wire end to the necessary temperature. To facilitate the compression operation, the wire end is first bent laterally so as to lie between the nozzle and the surface against which it is being pressed.

After attachment, the wire is trimmed by means of a shear-type cutting device, and the wire end issuing from the nozzle is then bent or crimped generally to the shape of a hook in preparation for the next thermocompressive bonding operation. The bending of the wire end can be effected by twisting the closed shear-like tool after cutting the wire and before releasing the wire end adjacent to the nozzle, so as to turn a portion of this end upwardly. The wire end thus bent and extending away from the axial direction of the wire is rather long so that it cannot be directly employed for attachment to small semiconductor areas, for example those having a length of less than 150 microns.

The length of the laterally bent end of the wire can be considerably reduced by adjusting the shear blades in such a manner that the overlapping motion of the blades that cause severing of the wire simultaneously effect the desired crimping of the wire end. Under most favorable conditions, the length of the wire end extending between the nozzle opening to the cutting plane is equal to the wire diameter plus the thickness of the scissors blade facing the nozzle. For example the length of the wire end portion is about 70 to 120 microns for a wire diameter of about microns and a shear blade thickness of 50 to 100 microns.

For bonding contact wires to the extremely small areas available on transistors and many other electronic semiconductor devices having a length of less than 100 microns, and preferably about 50 microns long, shorter lengths of contact wire are required, however, namely lengths of not more than and preferably less than about 40 microns. Such short lengths of the laterally bent wire protruding from the thermocompression nozzle have not been obtainable with methods and devices of the above-mentioned type heretofore, because the thickness of the cutter blade that is closer to the nozzle cannot be arbitrarily reduced without excessively impairing the necessary mechanical strength thereof.

It is an object of my invention to improve thermocompression methods and devices generally of the abovementioned kind, so as to effect, simultaneously with the thermo-compressive bonding of a wire to a semiconductor body, the formation of a laterally bent and sufficiently short end at the severed supply wire which directly permits this end to be thermocompressively bonded to a semiconductor member having relatively small contact area.

To this end and in accordance with my invention, the bonding of a contact wire to a semiconductor area, particularly an area of extremely small size, is effected generally in accordance with the aforementioned principles of the known method, namely by supplying the wire through a guiding nozzle, attaching the protruding wire end to the semiconductor member by thermocompression with the aid of a nozzle, and thereafter trimming the attached wire to a given length by means of a pair of shear blades. However, according to a feature of my invention, at least one of the shear blades is elastically yielding relative to the other in a direction perpendicular to the cutting plane and hence parallel to the axis of the wire or nozzle. The blades, furthermore, are set relative to each other so that they abut against each other during a cutting stroke but are given an angular cross section at the cutting front so that, due to the elasticity mentioned, the blade located at the side closer to the nozzle will ride up on and then glide over the other blade thereby bending the wire end protruding from the nozzle as the wire is being cut. Conjointly with the last-mentioned feature, the cutting plane is located at a distance from the nozzle that is shorter than the sum of the wire diameter plus the thickness of the elastically yieldable shear blade adjacent to the nozzle.

Preferably and according to another feature of my invention, the shear blades of the cutting device, or at least the one blade adjacent the nozzle, are made of elastic material such as spring or tool steel of sufficiently thin gauge as to be capable of yielding in a direction away from the other blade to ride up on and cuttingly glide along the other blade in the manner explained hereinabove.

According to a further feature of my invention, the front cutting face of the upper blade, i.e., adjacent to the nozzle, is provided with an angular cross section, the angle being at least substantially rectangular and preferably obtuse, having its apex pointing in the cutting direction toward the wire.

According to still another, preferred feature of the invention, the upper i.e. nozzle-adjacent, shear blade of the cutting tool is provided with a reinforcing member which increases the mechanical strength and rigidity of the blade in an area spaced from the cutting edge. The reinforcing member is preferably given a stepped shape so that it has a top portion receding from the blade-contacting bottom portion of the reinforcing member and adapted to the shape of the nozzle. This facilitates loeating the cutting plane at the desired short distance from the nozzle end and also permits using the reinforcing member as a calibrating or adjusting device for properly setting the blade with respect to the nozzle, this being particularly of advantage when using the thermocompression device for mass production.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention has been illustrated and described as method and device for bonding a contact wire to a semiconductor member, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes maybe made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the fol- 3, lowing description when read in connection with the drawings, in which:

FIG. 1 shows schematically and in perspective a device for attaching contact wires to semiconductor components.

FIGS. 2, 3 and 4 show partly in section and schematical- 1y three different stages of a cutting and bending operation as performed in a thermocompression device heretofore available; and

FIGS. 5, 6 and 7 show schematically and partly in section three different stages of a cutting and simultaneous bending operation performed in accordance with the method and with the aid of the means according to the invention.

The same reference numerals are applied in all the figures for respective corresponding elements.

FIG. 1 serves mainly for explaining the cutting operation in conjunction with the other figures. A semi-conductor device, in this case a mesa transistor 1, is placed upon a heated support to assume the temperature required for thermocompressioon. A suitable heated support is shown in application Serial No. 335,323, filed January 2, 1964, of which I am coinventer. The transistor 1 is to be joined with contact wire at the areas 2, 3 and 4. The wire is supplied through a nozzle 5 of glass or other suitable material having an axial capillary 25 through which it is guided. The wire -6 consists of gold and has a diameter of about 20 microns. A contact 7 on the area 4 is produced by pressing the end of wire 6 against the area 4 with the aid of the nozzle 5 which for this purpose is lowered under an area pressure between approximate limits of 5 and kg. per m-m. onto the transistor 1 that is simultaneously heated to a preferable temperature of about 200 to about 400 C. Thereafter the wire 6 is pulled out of the nozzle 5 and passed to contact area 22 where the wire is attached at 2.7 in the same manner. After the bonding is completed at 4 and 27, the nozzle 5 is moved sufficiently far away from the transistor 1, and the bonded wire 6 is trimmed by means of a cutter consisting substantially of a pair of shear blades 8 and 9 which simultaneously causes the end of the wire to be bent laterally in preparation for the next thermocompressive bonding operation. The thickness of the shear blades is 50 to 100 microns.

As shown in successive stages in FIGS. 2, 3 and 4 the wire portion projecting from the nozzle opening is bent as the wire is being severed from a wire portion that may or may not be attached to a semiconductor body. The bending is the result of the gliding movement which the top blade 8 performs relative to the bottom blade in the cutting direction, i.e. transverse to the axis of the wire or nozzle.

FIG. 2 shows the cutting device at the beginning of the severing operation. After the shear blades meet each other, the wire is trimmed and the wire end projecting from the nozzle becomes bent as indicated in FIG. 3. U1- timately the bent portion forms a hook 11, as shown in FIG. 4. The smallest possible length of the laterally bent wire end from the cut tip 12 to the access opening of the capillary 25, corresponding to the distance s1 in FIG. 4, is at best equal to the sum of the wire diameter a plus the thickness r of the blade 8. J

FIGS. 5, 6 and 7 show a cutting and bending device according to the invention in three sequential stages corresponding to those described above with reference to FIGS. 2, 3 and 4 respectively.

The two shear blades 8 and 9 as employed according to the invention,-are placed in respective positions that overlap each other along the nozzle or wire axis when the blades are disengaged from each other. However, at least one of the blades, namely the upper blade 8, is yieldable away from the lower blade and preferably consists of suitably elastic blade material. Furthermore, the cutting front face 13, 15 of the upper blade 8, which is closer to the nozzle 5 than the lower blade 9, is given an angular cross section so that the cutting front of blade 8 slopes downwardly at 15 from the top surface of the blade and upwardly at 13 from the bottom surface of the blade 8, thus forming at the apex of the angle a cutting edge that points in the cutting direction toward the wire (FIG. 5). The cutting edge of the blade 8 is located at or slightly above the height of the top surface of the counter blade 9, the lower portion 13 of the front face on blade 8 receding from the cutting edge. The angle between the two slopes 13 and 15 can be substantially rectangular but is preferably obtuse. For increasing the mechanical stability, the illustrated embodiment is provided with a stiifening or reinforcing structure 14 which is firmly joined 'by any suitable means, such as welding, brazing or the like, with the blade 8 on the top surface thereof but which is suitably spaced from the cutting front of the blade in order not to interfere with the resilience or elasticity of the blade that is required in the vicinity of the cutting front. The reinforcing structure 14 has a stepped appearance that includes a bottom shoulder portion projecting toward the nozzle axis. The shape of the reinforcing member conforms to that of the nozzle 5 to permit placing the blades as close as possible to the nozzle 5 and, if desired, using the reinforcing member 14 for the purpose of calibrating or adjusting the blades relative to the nozzle, as will be apparent from FIG. 7.

As the blades 8 and 9 move toward each other from the starting position shown in FIG. 5, the wire 6 is out between the respective cutting edges of the two blades. The stage obtaining directly after the completion of the cut is shown in FIG. 6. The end of the wire 6 protruding from the nozzle 5 has now become slightly bent by the advance of the slope 15, and by virtue of the receding slope 13 the elastic blade 8 has commenced climbing up on the blade 9, thus increasing the bending pressure against the end of the wire 6. As is apparent from FIG. 6, the length of the wire end extending from the nozzle 5 does not depend upon the thickness of the upper shear blade 8 but is determined by the distance of its cutting edge from the nozzle end 10. The length of the wire end, therefore, is smaller than the sum of the wire diameter and the upper blade thickness.

If the cutting front of the shear blade 8 is given a sufliciently large slope, the length of the severed and bent wire end can be reduced to values only slightly larger than the diameter d of the Wire 6.

FIG. 7 shows the ultimate position of the cutting device employed in the invention. The elastic blade 8 now rides up on the blade 9 and has completed its gliding movement in overlapping relation to the top surface of blade 9. This gliding motion has caused the end of wire 6 to be bent to the shape of a hook 11. The length of the wire end now protruding from the nozzle is approximately 40 microns, for example.

I claim:

1. The method of bonding a contact wire to a semiconductor member by thermocompression, which comprises supplying a contact wire through a guide nozzle, trimming the wire to a given length and simultaneously bending its end laterally by cutting the wire between shear :blades normally set to abut against each other but elastically yieldable perpendicularly to the cutting plane into an overlapping relation, and simultaneously keeping the length of the wire between the cutting location and the nozzle shorter than the sum of the wire diameter plus the thickness of the nozzle-adjacent shear blade, whereby the laterally bent end of the wire is of a predetermined short length readily bondable to a semiconductor member of relatively small bonding area.

2. In a device for bonding a contact wire to a semi conductor member by thermocompression, guide nozzle means for supplying a contact wire, and trimming means including a pair of shear blades spaced from said nozzle means and having a cutting plane located transversely to the axis of the wire, said blades being normally set to abut against each other but being elastically yieldable (I perpendicularly to said cutting plane into an overlapping relation for trimming the wire to a given length of which the wire portion between the cutting plane and said nozzle means is shorter than the sum of the wire diameter and the thickness of one of said blades and for simultaneously imparting to the extreme end portion of the wire a lateral bend of a predetermined short length readily attachable to a semiconductor member of relatively small attaching area.

3. In a device for bonding a contact Wire to a semiconductor member by thermocompression, guide nozzle means for supplying a contact wire, and trimming means including a pair of shear blades spaced from said nozzle means and having a cutting plane located transversely to the axis of the wire, said blades being normally set to abut against each other, and one of said blades having a cutting edge forming the apex of an angle pointing in the direction of cutting toward the axis of the wire, said one blade being elastically yieldable substantially perpendicularly to said Cutting plane when said blades are brought into abutment with each other, said apex of said one blade guiding the same into an overlapping position up and over the other of said blades for trimming the Wire to a given length of which the wire portion between the cutting plane and said nozzle mean-s is shorter than the sum of the wire diameter and the thickness of one of said blades and for simultaneously imparting to the extreme end portion of the wire a lateral bend of a predetermined short length readily attachable to a semiconductor member of relatively small attaching area.

4. In a device for bonding a contact wire to a semiconductor member by thermocompression, guide nozzle means for supplying a contact wire in a substantially vertically downward direction, and trimming means including a pair of shear blades located below and spaced from said nozzle means and having a cutting plane located substantially horizontally to the axis of the wire and of said nozzle means, one of said blades having a bottom face lower than the top face of the other of said blades in a normally set position thereof in which said blades tend to abut against each other, and said one blade having a cutting edge forming the apex of a solid angle pointing in the direction of cutting toward the axis of the wire, said one blade being elastically yieldable substantially vertically when said blades are brought into abutment with each other, said apex of said one blade guiding the same up and over the other of said blades into a mutually overlapping position with said other blade for trimming the wire to a predetermined length of which the wire portion between the cutting plane and said nozzle means is shorter than the sum of the wire diameter and the thickness of said one blade and for simultaneously imparting to the extreme end portion of the wire a lateral bend of a predetermined short length adapted to be readily bondable to a semiconductor member of rela tively small bonding area.

5. In a device for bonding a contact wire to a semiconductor member by thermocompression, guide nozzle means for supplying a contact wire, and trimming means including a pair of shear blades spaced from said nozzle means and having a cutting plane located transversely to the axis of the wire, said blades being normally set to abut against each other, one of said blades having a cutting side comprising a pair of mutually inclined faces forming the sides of an angle, the apex of said angle being the cutting edge of said one blade and being directed toward the axis of the wire, said one blade being elastically yieldable substantially perpendicularly to said cutting plane when said blades are brought into abutment with each other so that said apex of said one blade guides said one blade into an overlapping position up and over the other of said blades for trimming the wire to a given length in which the wire portion between said cutting plane and said nozzle means is shorter than the sum of the wire diameter and the thickness of said one blade and for simultaneously imparting to the extreme end portion of the wire a lateral bend of a predetermined short length adapted to be readily bendable to a semiconductor member of relatively small bonding area.

6. Device according to claim 5 wherein the angle be tween the mutually inclined cutting faces of said one blade is at least substantially a right angle.

'7. Device according to claim 5, wherein the angle between the mutually inclined faces of said one blade is obtuse.

8. Device according to claim 4 wherein said one blade has a top face, including blade reinforcing means located on said top face of said one blade.

9. Device according to claim 4 wherein said one blade has a top face, including a blade stiffening member secured to said top face and located at a distance from the cutting edge of said one blade.

114i. Device according to claim 9, said blade stiffening member having a stepped outline conforming to the outline of said nozzle means.

References Cited by the Examiner UNITED STATES PATENTS 314,845 3/ 1885 Hubbard 72464 3,128,648 4/ 1964 Clagett 228--44 3,186,446 6/1965 Hunt 140- 93 FOREIGN PATENTS 559,390 9/1932 Germany.

CHARLES W. LANHAM, Primary Examiner.

G. A. CROSBY, Assistant Examiner. 

2. IN A DEVICE FOR BONDING A CONTACT WIRE TO A SEMICONDUCTOR MEMBER BY THERMOCOMPRESSION, GUIDE NOZZLE MEANS FOR SUPPLYING A CONTACT WIRE, AND TRIMMING MEANS INCLUDING A PAIR OF SHEAR BLADES SPACED FROM SAID NOZZLE MEANS AND HAVING A CUTTING PLANE LOCATED TRANSVERSELY TO THE AXIS OF THE WIRE, SAID BLADES BEING NORMALLY SET TO ABUT AGAINST EACH OTHER BUT BEING ELASTICALLY YIELDABLE PERPENDICULARLY TO SAID CUTTING PLANE INTO AN OVERLAPPING RELATION FOR TRIMMING THE WIRE TO A GIVEN LENGTH OF WHICH THE WIRE PORTION BETWEEN THE CUTTING PLANE AND SAID NOZZLE MEANS IS SHORTER THAN THE SUM OF THE WIRE DIAMETER AND THE THICKNESS OF ONE OF SAID BLADES AND FOR SIMULTANEOUSLY IMPARTING TO THE EXTREME END PORTION OF THE WIRE A LATERAL BEND OF A PREDETERMINED SHORT LENGTH READILY ATTACHABLE TO A SEMICONDUCTOR MEMBER OF RELATIVELY SMALL ATTACHING AREA. 